Eirn (IPA ɛɹn) is the second of seven planets revolving around Hylissar's Lair, aka the Sun. It is the second largest of the four terrestrial planets, and the only one that contains liquid water. It has 2 large landmasses, and four smaller ones, as well as countless islands and atolls.

Eirn is the youngest of all seven planets, created by the gods during The Pact, billions of years after the natural formation of the Solar System.